This invention relates to lasers and, more particularly, to a laser having a relatively short, easily controlled annular resonator.
In a laser having a conventional unstable resonator, the generated electromagnetic energy is outcoupled by magnification. In other words, the resonator is designed to cause divergence of the energy passing through the gain medium until such energy spreads beyond the periphery of one of the reflectors of the resonators. The electromagnetic oscillations are sustained by feedback in the form of back reflections along the optical axis of the resonator.
To improve the uniformity of beam intensity in a chemical laser vis-a-vis a solid cylindrical gain medium, an annular gain medium is sometimes employed. In a laser having an annular gain medium and an annular unstable resonator, the feedback necessary to sustain oscillations is provided by diffraction at the inner edge of the reflector annulus. The feedback is increased to a sufficient level by spacing the reflectors of the resonator much further apart than the length of the gain medium, which greatly increases the size of the system vis-a-vis a laser that employs a solid cylindrical gain medium. Attempts have been made to reduce the size of such a laser by employing conical reflectors to fold the optical system of the resonator. Such measures create instability and render mode control difficult.